Apparatus for the control of combustion



March 7, 1933. o w LUSBY 1,900,884

APPARATUS FOR THE CONTROL OF COMBUSTION Filed June 23, 1931 4 2 Sheets-Sheet 1 'Fig.1

IN VEN TOR.

March 7, 1933. o. w. LUSBY APPARATUS FOR THE coumoh OF COMBUSTION 2 Sheets-Sheet 2 rm Euro Patented Mar. 7, 1933 UNITED STATES PATENT OFFICE OSCAR W. LUSBY, OI BALTIMORE,

APPARATUS FOR THE CONTROL OF COMBUSTION Application filed Jane 23,

This invention relates to combustion systems and particularly to automatic means for controlling the adnnssion of combustion air.

The invention is especially ada ted to combustion systems in which a com ustible gas of rapidly varying value is burned with air admitted thereto under pressure and it has for its general object the elimination of potential and sensible heat losses in systems of this kind by the provision of automatic means to maintain a substantially correct ratio between the volume of air and the volume of combustible gas so as to effect complete combustion of the gas without incurring excess sensible heat losses through the ad mission of excess air.

A particular object of the invention is to provide automatic mechanism for the control of the air introduced for burning combustibles of variable composition in order that the ratio of the volume of air to the volume of combustibles may be re lated so as to maintain at all times any esired excess of oxygen.

As is well known and understood the thermal content and specific gravity of manufactured and natural combustibles vary widely. Factors contributing to this variation in manufactured combustibles are the irregularity of the basic fuel and the varying conditions of normal manufacturing operations such as temperature changes and the changing quantity of air or steam introduced. The air required for combustion varies as the properties and nature of the combustible vary. For the complete and eflicient combustion of gaseous combustibles a small but definite excess of oxygen is required. If the excess of oxygen or air is large the combustion becomes inefficient on account of excess sensible heat loss.

It is proposed by the present invention to provide an automatic system for the control of the air supplied to the combustible which will accurately proportion the volume of air to the volume of combustible so as to substantially eliminate potential and excess sensible heat losses.

The invention will be described in connection with the combustion occurring in a gas 1881. Serial No. 546,246.

furnace of a usual type with the understanding, however, that in its broadest aspects the invention is by no means limited to this specific application and may be applied to the control of any system where the air re quirements are variable. I

Fig. 1 is a sectional view of a gas furnace showing in combination therewith elements of the invention; and

Fig. 2 is a diagrammatic view of a controlling system whi'ch may be employed in practicing the invention.

Referring to Fig. 1 which shows the invention as applied to one of the usual types of gas furnaces, the gas and air connections are shown at A, the path of the burning gases is shown by arrows and the sample tube for withdrawing a sample of the stack ases is shown at B. At C in the air line is s own a damper which is adapted to respond automatically to control the air admitted to the furnace in accordance with the amount of oxygen passing out the stack D. When the amount of oxygen increases above a fixed maximum the damper will partially close automatically or if the oxygen should fall below the desired minimum the damper opens.

The automatic system for controllin this damper is illustrated diagrammatica y in Fig. 2. Referring thereto, numeral 1 designates wall of the stack as shown in Fig. 1. This sampler tube is connected with a small two cylinder pump 2, electrically operated, one cvlinder of which draws the gas sample from the stack forcing it through the apparatus at a constant rate. Connected with the second cylinder of this pump through pipe 3 is a constant supply of hydrogen. As shown in a sampler tube inserted through the Fig. 2 the hydrogen may be generated electrolytically by a small generator represented diagrammatically at 4. The source of current for operating this generator is shown as a storage battery S. An adjustable resistance r and an ammeter a may be inserted in the connections to the generator to facilitate the maintenance .of a substantially constant current. An electric switch in the line cuts the current 0E the generator when not in use.

As an alternative arrangement a storage supply of hydrogen with a regulator to deliver the gas at constant pressure may be connected to pipe 3.

Both cylinders of the pump deliver into pipe 7 which is branched at 8, one branch including a cock 9, a combustion pipette 10, a tube 11 containing a suitable drying agent and one member 12 of a thermal conductivity cell of a known type such as the Engelhard cell; the other branch includes a cock 13, a drying tube 14, and another member 15 of said cell. The members 12 and 15 of the cell enclose fine quartz-incased platinum :oils 16 and 17, respectively, included in two of the arms of a lVheatstone bridge as clearly shown in Fig. 2,

the two remaining arms of the bridge contain adjustable resistances R and R. A battery F maintains a suitable difference of potential between the terminals of the bridge and a translating device, such as a galvanometer 18. is connected in the bridge wire and conresistance varied-if at trols the circuits of two relays 19 and 20, which in turn control the operation of an electric motor 21, connected through suitable reduction gearing with the damper 22.

The operation of the above described antomatic controlling system for the air supplied to a furnace is briefly as follows: Switches 5 and 6 are closed which starts the motor to the pump 2, energizes the hydrogen generator and places a potential on lines 23 and 24. One cylinder of the pump draws gases from the stack D forcing them at a constant rate through the apparatus. The other cylinder of the pump forces a definite amount of hydrogen into the system with the stack gases. The mixture of hydrogen and stack gases divides at 8, one part passing through the combustion pipette 10, the drying tube 11 and one arm, 12, of the lVheatstone bridge while the other passes through the dryer 14 and through the other arm, 15, of said brid e. if no oxygen is present in the stack gases, t e composition of the gaseous mixture will remain unaltered in passing through these two branches and gases of the same composition will be passed through the two members, 12 and 15, of the Wheatstone bridge and the heated cell coils, 16 and 17, being subjected to the same condition, will have their electrical all in exactly the same degree. The resistances R and R, however, are set so that under these conditions the bridge is unbalanced and a current will flow causing the galvanometer pointer to make contact with the stationary contact 25 with the result that relay 20 is energized, closing contacts 27 which will operate the motor 21 in 'such a way as to move the damper 22 towards its open position, increasing the amount of air introduced into the furnace. I

As the oxygen increases in the stack gas, the mixture of hydrogen and stack gases pumped through the branch of the apparatus containing the combustion pipette will be increasingly affected by the hydrogen combining with the oxygen. The amount of hydrogen removed is of course proportional to the oxygen in the gas. The gas passing through member 12 of the WVheatstone bridge will contain less hydrogen than that passing through the other member and since hydrogen has a high thermal conductivity, one side of the bridge will have a difi erent temperature from the other side and the electrical resistances of the coils 16 and 17 will be different. In this way as the oxygen in the stack gases increases the coils 17 and 16 become more unbalanced until finally they balance the resistances R and R which were originally fixed as unbalanced resistances. When the VVheatstone bridge is balanced the pointer of the galvanometer moves away from the contact- 25 and the motor 21 stops opening valve 22. If the oxygen in the stack gases should increase above a predetermined amount, for which the resistances R and R are set, the coils 16 and 17 become sufiiciently unbalanced to allow a current to flow through the galvanometer in the opposite direction and the pointer makes contact with 26 which ener-- gizes relay 19, causing the motor 21 to operate so as to close valve 22. As the oxygen decreases to the desired amount the bridge becomes balanced, the pointer moving away from contact 26 which stops the motor.

From the above description, it is evident that since the oxygen detecting apparatus may be made very sensitive and since its action is rapid, any variation of the oxygen in the stack gases either above or below the required amount may be quickly detected and corrected by the movement of the valve in the air line. This apparatus therefore insures that under substantially all conditions the proper predetermined amount of air for the efficient combustion of a variable combustible will be supplied.

lVhile the invention has been designed and described for eliminating potential and excess sensible heat losses in a usual type of gas furnace, it is not intended to restrict the scope or application to combustion systems of this particular kind. The broad results effected by the invention, viz. automatic control of the combustion air in accordance with the oxygen content of the combustion products, for the purpose of securing at all times the correct amount of air for any condition that may arise in the combustion process may be desirable in many different types of combustion systems to which the invention is easily applicable. Thus, for particular furnace operations it may be desirable to maintain definite reducing atmospheres or definite oxidizing atmospheres in which a predetermined deficiency or excess of oxygen is present, and it will be readily understood by one skilled in the art that this may readily be done merely by changing the extent to which the resistances R and R are unbalanced without in any way altering the application of my invention.

I claim:

1. In a combustion system, a passage way through which a combustible gas flows, means for admitting air to the gas stream to cause combustion thereof, means for diverting from the gaseouspioducts of combustion a small sample thereof, means for admixing with said sample a definite proportion of hydrogen, a thermal conductivity cell comprising two chambers each inclosing a metal filament, a Wheatstone bridge two of the armsof which respectively include said filaments, a conduit having two branches through which the gaseous mixture flows in substantially equal volumes, said branches respectively communicating with the two chambers of said cell, and one only of said branches including a combustion pipette, a galvanometer connected in said bridge and means controlled by saidgalvanometer for governing said first mentioned means.

2. In a combustion system, a gas passage into which air and a combustible gas of varying value are admitted, a sampler tube inserted into said passage at a point where combustion is substantially-complete, a source of hydrogen, a pipe connected to said tube and a pipe connected to said source of hydrogen, means for withdrawing through said pipes definite proportions of hydrogen and gaseous products of combustion respectively, a common pipe to which the gaseous mixture is delivered, the latter having two branches through which said mixture flows in substantially equal -.volumes, a thermal conductivity cell comprising two chambers respectively connected to said branches, each chamber inclosing a metallic filament, a combustion pipette in one of said branches, a Wheatstone bridge having two arms respectively including said filaments,'a galvanometer connectedin said bridge,'and means for governing the admission of .air to said gas'passage controlled by said galvanometer.

3. The method ofrconti'olling the nature of the products of combustion which comprises the automatic diversion of a portion of the gaseous combustion products, the mixing of the said portion with an excess of a hydrogen-containing gas and exposing at least a portion of the said mixture to a high temperature above the ignition point of the hydrogen-containing gas and controlling the elements of combustion and in consequence the nature of the products of combustion in accordance with the thermal conductivities of said mixture before and after exposure to high temperature.

4. The. method of effecting complete combustion without incurring excess sensible heat losses which comprises the automatic diverelements of combustion in accordance with a the thermal conductivities of the hydrogencombustion products mixture before and after exposure to high temperatures.

5. The method of controlling the oxidizing-reducing character of the products of combustion utilizing air which comprises the diversion of a portion of the gaseous combustion products, the mixing of the said portion with an excess of a hydrogen gas and exposing at least a portion of the said mixture to a temperature above the ignition point of hydrogen and controlling the air inlet to the combustion in accordance with the. thermal conductivity of said mixture.

6. The method of controlling the nature of the products of combustion which comprises the diversion of a portion of the gaseous combustion products, the mixing of the said portion withan excess of hydrogen containing gas, the exposure ofthe said mixture to a platinum wire heated to a temperature above the ignition point of hydrogen and controlling the elements of combustion in accordance with the thermal conductivities of said mixture before and after exposure to high temperature.

7 In a combustion system, means for admitting air to the material. to be burned; means for'diverting from the gaseous products of combustion a small sample thereof, means for admixing with said sample a definite proportion of hydrogen, means for dividing the gaseous mixture into two substantially equal streams and for causing the hydrogen and oxygen in one stream only to combine, two heated metallic filaments over which said streams respectively pass, means for measuring differences in the thermal conductivities between said streams due to the differences between the hydrogen content of said streams, and means controlled by said measuring means for governing first mentioncd means.-

OSCAR W. LUSBY. 

